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Understanding the microenvironment structure‐activity relationship of singlet‐atom catalysts (SACs) is imperative for the development of high‐performance photocatalytic devices. However, the challenge remains to finely regulate the coordination microenvironment of SACs. Herein, single‐atom Nx─Cu─O4‐x (x = 1–4) photocatalysts with different coordination environments are successfully prepared based on pre‐design reticular supramolecular covalent organic frameworks (COFs) for direct photocatalytic 1O2 production from O2. The results show that the high activity of Cu SACs is closely related to the N,O‐coordination microenvironment, which is primarily ascribed to the different electrophilicity of the N, O atom. The electron configuration of N3‐Cu‐O1 endows photocatalyst enhanced charge transfer capability and the nearest D‐band center to the Fermi level. The "end‐on" type adsorption configuration of O2 at the N3─Cu─O1 active site can promote the breaking of Cu─O bonds rather than O─O bonds. As a result, the N3‐Cu‐O1@COF photocatalyst exhibits the most optimal formation and desorption energies for intermediates •OOH, which provides an advantageous reaction pathway with fewer steps and a lower barrier for 1O2 production. This work highlights the structure‐activity relationship of SACs for long‐term applications. [ABSTRACT FROM AUTHOR]

Semihydrogenation of trace acetylene in an ethylene gas stream is a vital step for the industrial production of polyethylene, in which Pd single-site catalysts (SSCs) have great potential. Herein, two Pd SSCs with different coordination structures are prepared on hierarchical nitrogen-doped carbon nanocages (hNCNC) by regulating the nitrogen species with or without using dicyandiamide. With using dicyandiamide, the obtained Pd1-Ndicy/hNCNC SSC features the coordinated Pd by two pyridinic N and two pyrrolic N (PdN2pyN2pr). Without using dicyandiamide, the obtained Pd1/hNCNC SSC features the coordinated Pd by pyridinic N and C (PdNxpyC4−x, x = 1–4). The former exhibits an 18-fold increase in catalytic activity compared to the latter. Theoretical results reveal the abundant unoccupied orbital states above the Fermi level of PdN2pyN2pr moiety, which can facilitate the activation of substrate molecules and dynamics of acetylene hydrogenation as supported by the combined theoretical and experimental results. In addition, the PdN2pyN2pr moiety presents a favorable desorption of ethylene. Consequently, the Pd1-Ndicy/hNCNC SSC exhibits high C2H2 conversion (99%) and C2H4 selectivity (87%) at 160 °C. This study demonstrates the impact of Pd single-site coordination structure on catalytic performance, which is significant for the rational design of advanced Pd SSCs on carbon-based supports. [ABSTRACT FROM AUTHOR]

Efficient hydroboration of aldehydes and ketones is demonstrated using a single‐site MoO2 catalyst supported on activated carbon. Under mild conditions with low catalytic loadings, the reaction exhibits chemoselectivity towards carbonyl reduction over halides, alkene, alkyne, nitrile, and ester groups, affording high yields of desired products. Furthermore, competition studies between aldehyde and ketone reduction using HBpin and HBcat indicate that HBpin preferably functionalizes aldehydes, while HBcat can functionalize either substrate under specific conditions. Mechanistic studies suggest that the reaction proceeds via the initial formation of a molybdenum‐hydride species upon B−H activation and subsequent molybdenum‐alkoxide species upon carbonyl activation by the Mo center. The experimental activation energy of 14.3 kcal/mol alignssatisfactorily with the DFT computed ΔH≠ of 18.7 kcal/mol, further supporting the proposed mechanism. Combined experimental/computational analyses reveal that excess HBpin can possibly deactivate the catalyst. The presence of excess benzaldehyde efficiently mitigates deactivation by HBpin, providing significantly higher catalyst recyclability. Overall, this non‐toxic, air‐ and moisture‐stable, active, and selective catalyst demonstrates significant potential for green processes. [ABSTRACT FROM AUTHOR]

Black phosphorus (bP) is a two‐dimensional van der Waals material unique in its potential to serve as a support for single‐site catalysts due to its similarity to molecular phosphines, ligands quintessential in homogeneous catalysis. However, there is a scarcity of synthetic methods to install single metal centers on the bP lattice. Here, we demonstrate the functionalization of bP nanosheets with molecular Re and Mo complexes. A suite of characterization techniques, including infrared, X‐ray photoelectron and X‐ray absorption spectroscopy as well as scanning transmission electron microscopy corroborate that the functionalized nanosheets contain a high density of discrete metal centers directly bound to the bP surface. Moreover, the supported metal centers are chemically accessible and can undergo ligand exchange transformations without detaching from the surface. The steric and electronic properties of bP as a ligand are estimated with respect to molecular phosphines. Sterically, bP resembles tri(tolyl)phosphine when monodentate to a metal center, and bis(diphenylphosphino)propane when bidentate, whereas electronically bP is a σ‐donor as strong as a trialkyl phosphine. This work is foundational in elucidating the nature of black phosphorus as a ligand and underscores the viability of using bP as a basis for single‐site catalysts. [ABSTRACT FROM AUTHOR]

Samples of model single-site catalysts based on iridium and rhodium were synthesized by immobilizing the complexes [Ir(COD)(IMes)Cl] and [Rh(COD)(IMes)Cl] (where COD is 1,5-cyclooctadiene and IMes is 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) on silica, the surface of which was modified with a linker containing a diphenylphosphine group (Ph2P). The supports were silicon plates with a flat surface coated with a layer of natural oxide 1–3 nm thick (Si–SiO2(nat)) or with a specially grown SiO2 film (∼300 nm) (Si–SiO2(ox)). The states of chemical elements in the modified silicon plates and samples of model catalysts were determined by XPS. Based on the results obtained, the nature of the coordination of the immobilized complexes was assumed. Samples of the catalysts were tested in the reaction of gas-phase hydrogenation of propene with parahydrogen. [ABSTRACT FROM AUTHOR]

Atomically‐dispersed heterogeneous metal catalysts can be considered as an "upgraded" version of classical solid metal catalysts. Unlike traditional heterogeneous metallic catalysts that contain nanoparticles or bulk micro‐sized transition metal species, the active sites of these novel types of catalysts are atomically distributed on the support's surface. This provides several advantages compared to classical catalysts such as higher activity and need for just very small amounts of metal precursors for the catalyst preparation. The latter issue is a key point in green chemical processes and of importance to achieve low‐cost pathways for industrial‐scale synthesis. The atomically dispersed metal sites permit a maximum of metal dispersion and additionally allow to achieve more reproducible heterogeneous catalysts. This review summarizes an overview on breakthrough findings in synthesis, applications and characterization techniques developed in the area of single‐atom, dual‐atom, single‐atom‐layer, single‐site as well as single‐atom nanozyme/enzyme catalysis. The characteristics and properties of each system provide an appropriate understanding for designing a nanomaterial that is optimized for a specific requirement. [ABSTRACT FROM AUTHOR]

Immobilized [Ir(COD)Cl]2-Linker/TiO2 catalysts with linkers containing Py, P(Ph)2 and N(CH3)2 functional groups were prepared. The catalysts were tested via propene hydrogenation with parahydrogen in a temperature range from 40 °C to 120 °C which was monitored via NMR. The catalytic behavior of [Ir(COD)Cl]2-Linker/TiO2 is explained on the basis of quantitative and qualitative XPS data analysis performed for the catalysts before and after the reaction at 120 °C. It is shown that the temperature dependence of propene conversion and the enhancement of the NMR signal are explained via a combination of the stabilities of both the linker and immobilized [Ir(COD)Cl]2 complex. It is demonstrated that the N(CH3)2-linker is the most stable at the surface of TiO2 under used reaction conditions. As a result, only this sample shows a rise in the enhancement of the NMR signal in the 100–120 °C temperature range. [ABSTRACT FROM AUTHOR]

Electrochemical nitrate reduction to ammonia powered by renewable electricity is not only a promising alternative to the established energy‐intense and non‐ecofriendly Haber–Bosch reaction for ammonia generation but also a future contributor to the ever‐more important denitrification schemes. Nevertheless, this reaction is still impeded by the lack of understanding for the underlying reaction mechanism on the molecular scale which is necessary for the rational design of active, selective, and stable electrocatalysts. Herein, a novel single‐site bismuth catalyst (Bi‐N‐C) for nitrate electroreduction is reported to produce ammonia with maximum Faradaic efficiency of 88.7% and at a high rate of 1.38 mg h−1 mgcat−1 at −0.35 V versus reversible hydrogen electrode (RHE). The active center (described as BiN2C2) is uncovered by detailed structural analysis. Coupled density functional theory calculations are applied to analyze the reaction mechanism and potential rate‐limiting steps for nitrate reduction based on the BiN2C2 model. The findings highlight the importance of model catalysts to utilize the potential of nitrate reduction as a new‐generation nitrogen‐management technology based on the construction of efficient active sites. [ABSTRACT FROM AUTHOR]

When early transition metal complexes are molecularly grafted onto catalyst supports, well‐defined, surface‐bound species are created, which are highly active and selective single‐site heterogeneous catalysts (SSHCs) for diverse chemical transformations. In this minireview, we analyze and summarize a less conventional type of SSHC in which molybdenum dioxo species are grafted onto unusual carbon‐unsaturated scaffolds, such as activated carbon, reduced graphene oxide, and carbon nanohorns. The choice of earth‐abundant, low‐toxicity, versatile metal constituents, and various carbon supports illustrates "catalyst by design" principles and yields insights into new catalytic systems of both academic and technological interest. Here, we summarize experimental and computational investigations of the bonding, electronic structure, reaction scope, and mechanistic pathways of these unusual catalysts. [ABSTRACT FROM AUTHOR]

Sulfur poisoning and regeneration are global challenges for metal catalysts even at the ppm level. The sulfur poisoning of single‐metal‐site catalysts and their regeneration is worthy of further study. Herein, sulfur poisoning and self‐recovery are first presented on an industrialized single‐Rh‐site catalyst (Rh1/POPs). A decreased turnover frequency of Rh1/POPs from 4317 h−1 to 318 h−1 was observed in a 1000 ppm H2S co‐feed for ethylene hydroformylation, but it self‐recovered to 4527 h−1 after withdrawal of H2S, whereas the rhodium nanoparticles demonstrated poor activity and self‐recovery ability. H2S reduced the charge density of the single Rh atom and lowered its Gibbs free energy with the formation of inactive (SH)Rh(CO)(PPh3‐frame)2, which could be regenerated to active HRh(CO)(PPh3‐frame)2 after withdrawing H2S. The mechanism and the sulfur‐related structure–activity relationship were highlighted. This work provides an understanding of heterogeneous ethylene hydroformylation and sulfur‐poisoned regeneration in the science of single‐atom catalysts. [ABSTRACT FROM AUTHOR]

Photothermal catalytic conversion of waste plastics into fuels and/or feedstocks using renewable solar energy can achieve solar‐to‐chemical conversion, resource sustainability, and environmental remediation simultaneously. However, the construction of photothermal catalysts with strong light absorption and high catalytic activity remains a great challenge. In this work, integrated cobalt single‐site catalysts (Co SSCs), coupled with strong photothermal conversion, high catalytic activity, and stability, are employed to catalyze the glycolysis of polyesters. The unique coordination‐unsaturated CoO5 single‐site can coordinate with the carbonyl groups in polyester, thus boosting the nucleophilic addition elimination processes. As a result, the space‐time yield of Co SSCs is an order of magnitude higher than that of general catalysts. In addition, the polyethylene terephthalate (PET) conversion and bis(2‐hydroxyethyl) terephthalate yield in photothermal catalysis are 5.4 and 6.6 times higher than those of thermal catalysis under the same conditions, which are contributed by the localized heating effect. Technical economic analysis shows that the recycling of 105 tons of waste PET by photothermal catalysis consumes 146.4 GW·h electrical energy and misses 7.44 × 104 tons of CO2 emission. Therefore, a high‐efficient photothermal catalytic plastic recycling system is of great significance for waste plastic valorization. [ABSTRACT FROM AUTHOR]

Tandem catalysis stands out as a major instrument towards the intensification of existing and future chemical processes. Initially formulated in the field of homogeneous catalysis, the concept relies on the single‐pot integration of two (or more) catalysts showing high specificity for mechanistically decoupled reactions, while being operational and compatible under a single set of operation conditions. Isolated metal atoms stabilized on solid carriers in single‐atom catalysts (SACs) hold the potential to reconcile the high reaction specificities of mononuclear sites in molecular catalysts with an intrinsic catalyst compartmentalization on inorganic matrices. Understandably, SACs have started to be considered as platforms in tandem catalysis. Tandem (electro)catalytic processes based on SACs have been showcased recently. While this sets excellent prospects for the expansion of this research subarea, challenges are faced, particularly as to the verification of the tandem nature of the processes. [ABSTRACT FROM AUTHOR]

Ammonia synthesis via nitrate electroreduction is more attractive and sustainable than the energy-extensive Haber-Bosch process and intrinsically sluggish nitrogen electroreduction. Herein, we have designed a single-site Cu catalyst on hierarchical nitrogen-doped carbon nanocage support (Cu 1 /hNCNC) for nitrate electroreduction, which achieves an ultrahigh ammonia yield rate (YR NH3 ) of 99.4 mol h -1 g Cu -1 (2.30 mol h -1 g cat. ) of 99.3%, far beyond the most reported single-site catalysts on carbon-based supports. The combined -1 ) with ammonia Faradaic efficiency (FE NH3 ) of 99.3%, far beyond the most reported single-site catalysts on carbon-based supports. The combined operando characterization and theoretical studies indicate that the in situ formed Cu-cluster active sites are responsible for the high YR NH3 and FE NH3 due to the enhanced NO 3 - adsorption and subsequent protonation on the unique Cu 3 -N 4 moieties, and meanwhile, the hierarchical hNCNC support facilitates the mass/charge transfer kinetics, thus promoting the high expression of intrinsic activity. The demonstration of plasma N 2 oxidization and nitrate electroreduction cascade reaction manifests the great potential of the Cu 1 /hNCNC electrocatalyst in sustainable NH 3 synthesis. These findings offer valuable insights into the design of effective catalysts for electrosynthetic reactions.

This Review provides a summary of the use and the role of coordination complexes as precursors for the generation of heterogeneous catalysts for oxidation reactions of interest for fine chemical synthesis. Specific attention is paid to the comprehension of phenomena explaining the formation of active sites in heterogeneous catalysts. Different families of coordination precursors are considered. For each example, a brief critical description of the synthesis, characterization, and catalytic performance is reported. Special attention is paid to the chemical environment of the first coordination sphere of the active metal centre. The catalysts obtained by heterogenization, grafting, or anchoring of homogeneous catalysts can therefore exhibit enhanced catalytic performance by merging advantages of both homogeneous and heterogeneous systems. The deposition of coordination complexes over a preformed support is indeed a conceptually versatile strategy to design novel catalysts with tuned and controlled properties. [ABSTRACT FROM AUTHOR]

Olefin and diene transformations, catalyzed by organoaluminum-activated metal complexes, are widely used in synthetic organic chemistry and form the basis of major petrochemical processes. However, the role of M–(μ-Cl)–Al bonding, being proven for certain >C=C< functionalization reactions, remains unclear and debated for essentially more important industrial processes such as oligomerization and polymerization of α-olefins and conjugated dienes. Numerous publications indirectly point at the significance of M–(μ-Cl)–Al bonding in Ziegler–Natta and related transformations, but only a few studies contain experimental or at least theoretical evidence of the involvement of M–(μ-Cl)–Al species into catalytic cycles. In the present review, we have compiled data on the formation of M–(μ-Cl)–Al complexes (M = Ti, Zr, V, Cr, Ni), their molecular structure, and reactivity towards olefins and dienes. The possible role of similar complexes in the functionalization, oligomerization and polymerization of α-olefins and dienes is discussed in the present review through the prism of the further development of Ziegler–Natta processes and beyond. [ABSTRACT FROM AUTHOR]

The atomically dispersed Fe3+ sites of Fe−N−C single-site catalysts (SSCs) are demonstrated as the active sites for CO2 electroreduction (CO2RR) to CO but suffer from the reduction to Fe2+ at ∼ −0.5 V, accompanied by the drop of CO faradaic efficiency (FECO) and deterioration of partial current (JCO). Herein, we report the construction of F-doped Fe−N−C SSCs and the electron-withdrawing character of fluorine could stabilize Fe3+ sites, which promotes the FECO from the volcano-like highest value (88.2%@−0.40 V) to the high plateau (> 88.5%@−0.40–−0.60 V), with a much-increased JCO (from 3.24 to 11.23 mA·cm−2). The enhancement is ascribed to the thermodynamically facilitated CO2RR and suppressed competing hydrogen evolution reaction, as well as the kinetically increased electroactive surface area and improved charge transfer, due to the stabilized Fe3+ sites and enriched defects by fluorine doping. This finding provides an efficient strategy to enhance the CO2RR performance of Fe−N−C SSCs by stabilizing Fe3+. [ABSTRACT FROM AUTHOR]

Metal single-site catalysts have recently played an essential role in catalysis due to their enhanced activity, selectivity, and precise reaction control compared to those of conventional metal cluster catalysts. However, the rational design and catalytic application of metal single-site catalysts are still in the early stages of development. In this contribution, we report the rational design of Fe single sites incorporated in a hierarchical ZSM-5 via atomic layer deposition (ALD). The designer catalysts demonstrated highly dispersed Fe species, predominantly stabilized by oxygen atoms in the zeolite framework at terminal, isolated, and vicinal silanol groups within the micropores and external surfaces of the zeolite. The successful incorporation of highly thermally stable and uniform Fe single sites into hierarchical zeolite through ALD represents a significant advancement in few-walled carbon nanotube production. The inner and outer diameters of produced CNTs are approximately 4.4 ± 2.4 and 8.6 ± 1.8 nm, respectively, notably smaller than those produced via traditional impregnated catalysts. This example emphasizes the concept of rational design of a single Fe site dispersed on a hierarchical ZSM-5 surface, which is anticipated to be a promising catalyst for advancing catalytic applications.

Metal-nitrogen-carbon materials are promising catalysts for CO2 electroreduction to CO. Herein, by taking the unique hierarchical carbon nanocages as the support, an advanced nickel-nitrogen-carbon single-site catalyst is conveniently prepared by pyrolyzing the mixture of NiCl2 and phenanthroline, which exhibits a Faradaic efficiency plateau of > 87% in a wide potential window of −0.6–−1.0 V. Further S-doping by adding KSCN into the precursor much enhances the CO specific current density by 68%, up to 37.5 A·g−1 at −0.8 V, along with an improved CO Faradaic efficiency plateau of > 90%. Such an enhancement can be ascribed to the facilitated CO pathway and suppressed hydrogen evolution from thermodynamic viewpoint as well as the increased electroactive surface area and improved charge transfer fromkinetic viewpoint due to the S-doping. This study demonstrates a simple and effective approach to advanced electrocatalysts by synergetic modification of the porous carbon-based support and electronic structure of the active sites. [ABSTRACT FROM AUTHOR]

New ansa -zirconocene with bis(inden-2-yloxy)dimethylsilane ligand was synthesized and characterized by NMR spectroscopy and X-ray crystallography. The zirconocene was found to be highly active catalyst of ethylene polymerization and ethylene/hex-1-ene copolymerization upon methylaluminoxane activation. [ABSTRACT FROM AUTHOR]

The single‐site catalyst (SSC) characteristic of atomically dispersed active centers will not only maximize the catalytic activity, but also provide a promising platform for establishing the structure–activity relationship. However, arbitrary arrangements of active sites in the existed SSCs make it difficult for mechanism understanding and performance optimization. Now, a well‐defined ultrathin SSC is fabricated by assembly of metal‐porphyrin molecules, which enables the precise identification of the active sites for d‐orbital energy engineering. The activity of as‐assembled products for electrocatalytic CO2 reduction is significantly promoted via lifting up the energy level of metal dz2 orbitals, exhibiting a remarkable Faradaic efficiency of 96 % at the overpotential of 500 mV. Furthermore, a turnover frequency of 4.21 s−1 is achieved with negligible decay over 48 h. [ABSTRACT FROM AUTHOR]

• Grafting Pd(II) methyl complexes on silica provides well defined uniform Pd-centers. • The molecularly dispersed catalysts showed highest performance in Heck couplings. • They excelled performance of Pd(II) particles activating aryl chlorides drastically. • The ligand sphere of the palladium surface complexes directly affects their activity. Supported catalysts with molecularly dispersed, uniform palladium species were synthesized by the method of grafting. New specific synthesis protocols were developed in order to exclude self-reduction and agglomeration of palladium during immobilization. The successful synthesis of isolated mononuclear palladium(II) surface complexes of uniform structure was confirmed by MAS NMR, infrared spectroscopy and elemental analysis. The catalytic potential of these single-site catalysts for the Heck reaction was directly compared to well-characterized supported palladium oxide materials known and reported for their extraordinarily high activity in the conversion of aryl bromides. In contrast to those, the immobilized palladium surface complexes were able to quantitatively convert demanding non-activated aryl chlorides as substrates with conversions up to 62% and high selectivity. Although believed to be only pre-catalysts, the ligand sphere of the surface complexes directly affects their activity. The time-resolved reaction of chlorobenzene with styrene revealed that catalysts with supported amine complexes are able to constantly convert chlorobenzene during several hours of reaction time. It is proposed that the catalysts continuously provide active, dissolved Pd(0) species during the whole course of reaction. [ABSTRACT FROM AUTHOR]

Graphical abstract A series of Cu(II) complexes supported by bearing N -substituted phenylethanamine derivatives have been synthesised and characterised by X-ray diffraction. The distorted square planner Cu(II) complexes crystallized in dimeric form with two diastereomeric asymmetric units, i.e. (S C , S N and S C R N). Alkoxy derivatives, generated in situ , effectively polymerised rac -LA in controlled fashion yielding hetero-enriched PLA (P r = 0.86). The ROP activity of the current system largely rely on steric hindrance imposed by the substituents attached to ligand architecture. Abstract A series of Cu(II) complexes, [L n CuCl 2 ] 2 (L n = (S)- N -((1H-pyrazol-1-yl)methyl)-1-phenylethanamine (L1), (S)- N -((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-1-phenylethanamine (L2) and (S)-1-phenyl- N -((pyridin-2-yl)methyl)ethanamine (L3)) were synthesised and characterised. X-ray diffraction analysis revealed that the molecular structures of these distorted square planar Cu(II) complexes were dimeric with two asymmetric units crystallised in the (S C , S N) and (S C , R N) configurations. These are rare examples of dimeric Cu(II) complexes. The alkoxide derivatives, generated in situ , catalysed the ring-opening polymerisation of rac -lactide in a controlled fashion and displayed high activities (2 or 3 min for complete conversion). Heterotactic-enriched polylactide (with P r up to 0.86) was formed using these initiators at room temperature in CH 2 Cl 2. [ABSTRACT FROM AUTHOR]

[Display omitted] DFT simulations of ethylene polymerization with the participation of neutral Zr–Al3 hydride species revealed a fundamental difference in catalytic behaviour of triisobutylaluminium-activated heterocenes and conventional ansa- zirconocenes. [ABSTRACT FROM AUTHOR]

Owing to its capacity for reversible hydrogen storage, formic acid (FA) holds great promise as an alternative energy carrier to conventional fossil fuel systems. Whereas the decomposition of FA to hydrogen (H2) and carbon dioxide (CO2) through homogeneous catalysis is well established, the selective and efficient dehydrogenation of FA by a robust heterogeneous catalyst remains a challenge. A new heterogeneous ruthenium pincer framework with single-atomic sites was prepared in one step by the direct knitting of a phosphorus–nitrogen PN3Ppincer ruthenium complex in a porous organic polymer. The heterogeneous ruthenium complex efficiently dehydrogenates formic acid in both organic and aqueous media with remarkably enhanced stability. Notably, no detectable CO was generated and a turnover number (TON) of 145 300 was attained in a continuous experiment with no significant decline in catalytic activity (in sharp contrast, a total TON of only 5600 was obtained with the homogeneous analog under the same conditions). The single-atomic sites in the porous framework combined the desirable attributes of high reactivity and selectivity of a homogeneous catalyst with the significantly enhanced catalyst stability and reusability benefits of heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

Abstract: Porous CoNC catalysts with ultrahigh surface area are highly required for catalytic reactions. Here, a scale‐up method to synthesize gram‐quantities of isolated Co single‐site catalysts anchored on N‐doped porous carbon nanobelt (Co‐ISA/CNB) by pyrolysis of biomass‐derived chitosan is reported. The usage of ZnCl2 and CoCl2 salts as effective activation–graphitization agents can introduce a porous belt‐like nanostructure with ultrahigh specific surface area (2513 m2 g−1) and high graphitization degree. Spherical aberration correction electron microscopy and X‐ray absorption fine structure analysis reveal that Co species are present as isolated single sites and stabilized by nitrogen in CoN4 structure. All these characters make Co‐ISA/CNB an efficient catalyst for selective oxidation of aromatic alkanes at room temperature. For oxidation of ethylbenzene, the Co‐ISA/CNB catalysts yield a conversion up to 98% with 99% selectivity, while Co nanoparticles are inert. Density functional theory calculations reveal that the generated CoO centers on isolated Co single sites are responsible for the excellent catalytic efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Isolated, coordinatively unsaturated metal sites within metal-organic framework (MOF) materials feature interesting chemical properties and offer applications as single-site catalysts. Here, we report on the recent progress in providing fundamental insight into chemical reactions occurring inside MOFs. In addition to the common form, powders, we discuss the potential of MOF thin films (SURMOFs). The combined spectroscopic and modeling approach applied to selected systems demonstrated that the catalytic activity of MOFs can be precisely tuned. A particular interesting case is the so-called defect-engineering, where structural imperfections are created in a controlled fashion. The chemical properties of MOF materials can be further modified by integration and decoration of linkers or loading with guest species, such as metal or metal-oxide nanoparticles or nanoclusters. A particularly interesting aspect of layer-by-layer approaches for the fabrication of MOF thin films is the prospect to realize tandem catalysts.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Unlike Co clusters, isolated Co atoms have been shown to be selective for catalytic dehydrogenation of ethane to ethylene; however, preparation of isolated Co sites requires special preparation procedures. Here, we demonstrate that Atomic Layer Deposition (ALD) of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)cobalt(III) (Co(TMHD)3) on silica and other supports is effective in producing these isolated species. Silica-supported catalysts prepared with one ALD cycle showed ethylene selectivities greater than 96% at 923 K and were stable when CO2 was co-fed with the ethane. Co catalysts prepared by impregnation formed clusters that were significantly less active, selective, and stable. Rates and selectivities also decreased for catalysts with multiple ALD cycles. Isolated Co catalysts prepared on Al2O3 and MgAl2O4 showed reasonable selectivity for ethane dehydrogenation but were not as effective as their silica counterpart.

Zirconocene-mediated selective dimerization of α-olefins usually occurs when precatalyst (η5-C5H5)2ZrCl2 is activated by minimal excess of methylalumoxane (MAO). In this paper, we present the results of density functional theory (DFT) simulation of the initiation, propagation, and termination stages of dimerization and oligomerization of propylene within the framework of Zr-Al binuclear mechanism at M-06x/DGDZVP level of theory. The results of the analysis of the reaction profiles allow to explain experimental facts such as oligomerization of α-olefins at high MAO/(η5-C5H5)2ZrCl2 ratios and increase of the selectivity of dimerization in the presence of R2AlCl. The results of DFT simulations confirm the crucial role of the presence of chloride in the selectivity of dimerization. The molecular hydrogen was found in silico and proven experimentally as an effective agent that increases the rate and selectivity of dimerization.

[Display omitted] • The distribution of Rh species on the "29" oxide is heterogeneous while it is uniform for Pt. • The relative interaction strengths toward Cu and O determine adatom mobility. • Adatom mobility is proportional to the energy cost to distort the oxide layer. • Cohesion between metals and shallow potential energy surface expedite clustering. The dynamical nature of single-site catalysts under non-equilibrium conditions poses significant challenges in the full characterization of their active sites. The "29" oxide is a thin Cu x O film grown on Cu(1 1 1) which provides a well-defined surface on which to study the structure and chemistry of atomically dispersed precious metals. A combination of experimental and first-principles approaches is used to investigate the factors that influence the mobility of metal adatoms and their clustering tendencies. Our work elucidates how a homogenous coordination environment of neutral single-atoms can be obtained when its tendency to break oxide bonds within its vicinity is low. We demonstrate that this in turn affects the chemical activity of atomically dispersed species on thin-film oxides, as defects on the oxide would in fact allow such species to be more accessible to CO. We thus highlight the importance of understanding the relationship between defects and atomically dispersed active sites upon designing single-site catalysts. [ABSTRACT FROM AUTHOR]

Metal nanoparticles deposited on N-doped carbon materials have emerged as novel catalysts for various organic transformations. In this Minireview, strategies for the synthesis of metal composites on N-doped carbon supports and their state-of-the-art characterization are briefly described. The catalytic application of these fascinating materials in several industrially relevant reactions, including oxidations, hydrogenations, Fischer-Tropsch syntheses, and H2 generation, is also summarized. Furthermore, the effects of nitrogen incorporation on the different catalytic systems are highlighted. [ABSTRACT FROM AUTHOR]

The dimerization of 1-hexene was catalyzed by ten zirconocenes. High catalytic productivity was achieved via a two-step activation process, namely, the treatment of the zirconocene with triisobutylaluminum (TIBA) followed by methylaluminoxane (MAO). The zirconocene [(C 5 H 4 SiMe 2 ) 2 O]ZrCl 2 (10) exhibits a higher productivity and selectivity to dimer formation than the unsubstituted (C 5 H 5 ) 2 ZrCl 2 (1) complex. For the ansa -[Z(C 5 H 4 ) 2 ]ZrCl 2 complexes, the catalytic activity increases as the angle between the cyclopentadienyl rings decreases. The dimerization selectivity of 10 reaches 94% when the reaction is performed using Et 2 AlCl as the chlorine source needed to form the catalytic species. The possible mechanism of selective α-olefin dimerization is discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Supported titanium oxide species are active photocatalysts for selective oxidation of 2-propanol. • Activity and selectivity are a function of the titania loading. • Acetate formation as side reaction causes deactivation of bulk titania. • Supported titanium oxide species do not suffer deactivation by acetate formation. The photocatalytic performance of titanium oxide species supported on mesoporous silica (SBA-15) in the selective oxidation of 2-propanol is studied systematically as function of the titania surface loading. Monomers and oligomers of the supported titanium oxide species are formed on the silica surface in differing amounts with increasing loading, and the photocatalytic activity shows a strong dependence on the titanium content. A general advantage of supported samples in terms of net productivity could not be observed, but the photocatalysts' longevity and selectivity improve with lower degrees of oligomerization. In-situ infrared spectroscopy in diffuse reflectance under irradiation revealed a likely explanation for this observation: The relative probability of the overoxidation of 2-propanol to acetate and possibly even total oxidation to CO 2 increases with loading and is most severe for crystalline bulk titania. Stably adsorbed acetate appears to block the active sites on crystalline TiO 2 , but it is tolerable to a certain extent for the silica-supported samples. This work provides fundamental knowledge for the development of more stable and selective oxidation photocatalysts. [ABSTRACT FROM AUTHOR]

Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A stable site-isolated mononuclear platinum catalyst with a well-defined structure is presented. Platinum complexes supported in zeolite KLTL were synthesized from [Pt(NH3)4](NO3)2, oxidized at 633 K, and used to catalyze CO oxidation. IR and X-ray absorption spectra and electron micrographs determine the structures and locations of the platinum complexes in the zeolite pores, demonstrate the platinum-support bonding, and show that the platinum remained site isolated after oxidation and catalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • The possibility of loading Rh on organic linkers of MOFs for hydroformylation was investigated. • The most suitable MOFs structures (P-doped) for chelating Rh was found. • N -doped MOFs structures have the potential to catalyze hydroformylation, but the linear/branched ratio is poor. In this work, five different ligands for MOFs catalyzing 1-butene hydroformylation reactions were investigated using density functional theory (DFT) with heteroatoms (N, O, P) containing in the organic ligands that can chelate the catalytic metal Rh. The results show that the N/P-containing organic linkers have lower activation barriers than the carboxylate linkers (O-containing) and have potential for catalytic hydroformylation reactions. However, the N-containing catalysts have a significant defect in the selectivity of linear/branched product. The relatively low regioselectivity may be due to their weak steric effect of ligands. This work explores the strategy that MOFs fixing the single metal atom at metallolinkers for catalytic hydroformylation of 1-butene. It is of great significance for the design and construction of MOFs for hydroformylation in the future investigation. [ABSTRACT FROM AUTHOR]

A carbon nanotube (CNT) supported single-site Fe-N-C catalyst (CNTs/Fe-N-C) exhibited attractive properties in peroxidase (POD)-like activity and photothermal effect. Herein, we designed a therapeutic platform by wrapping doxorubicin (DOX) in mesoporous CNTs/Fe-N-C with the cell membrane (CM) of breast cancer. The ultimate nanoagent (CNTs/Fe-N-C/DOX/CM) exhibited high antitumor activity on account of its efficient catalytic ability, increased drug release rates, and significant photothermal effect. Due to the POD-like activity, CNTs/Fe-N-C could effectively catalyze hydrogen peroxide (H 2 O 2 ) into cytotoxic hydroxyl radicals ( • OH) for chemodynamic therapy (CDT) of the tumor. Besides, the released DOX not only merely induced the diagnosis of the tumor cells for chemotherapy (CT) but also generated H 2 O 2 to promote CDT. Moreover, the photothermal effect of the nanoagent could use for photothermal therapy (PTT). The increasing temperature was conducive to the release of DOX from micropore into the cell, which indirectly enhanced CT and CDT effects. As an intelligent and multifunctional drug delivery platform, the present CNTs/Fe-N-C/DOX/CM nanoagent could be engineered with synergistic treatments and favorable biosafety, which provides a promising paradigm in site-specific antitumor treatment and biomedicine.

An approach for the control and understanding of supported molecular catalysts is demonstrated with the design and synthesis of open and closed variants of a grafted Lewis acid active site, consisting of Al(III)-calix[4]arene complexes on the surface of silica. The calixarene acts as a molecular template that enforces open and closed resting-state coordination geometries surrounding the metal active sites, due to its lower-rim substituents as well as site isolation by virtue of its steric bulk. These sites are characterized and used to elucidate mechanistic details and connectivity requirements for reactions involving hydride and oxo transfer. The consequence of controlling open versus closed configurations of the grafted Lewis acid site is demonstrated by the complete lack of observed activity of the closed site for Meerwein-Ponndorf-Verley (MPV) reduction; whereas, the open variant of this catalyst has an MPV reduction activity that is virtually identical to previously reported soluble molecular Al(III)-calix[4]arene catalysts. In contrast, for olef in epoxidation using tert-butyl-hydroperoxide as oxidant, the open and closed catalysts exhibit similar activity. This observation suggests that for olefin epoxidation catalysis using Lewis acids as catalyst and organic hydroperoxide as oxidant, covalent binding of the hydroperoxide is not required, and instead dative coordination to the Lewis acid center is sufficient for catalytic oxo transfer. This latter result is supported by density functional theory calculations of the transition state for olefin epoxidation catalysis, using molecular analogs of the open and closed catalysts. [ABSTRACT FROM AUTHOR]

This review generalizes the data on the application of single-site catalysts (SSCs) in the industrial production of polyethylene. The history of their industrial application, the basic types of SSCs, the main processes of the production of polyethylene (PE) on the mentioned systems, the largest PE production plants using SSCs, and the application fields of polymers synthesized at these plants are described. The prospects for further development in this direction are discussed. [ABSTRACT FROM AUTHOR]